Star-delta starter cabinets
- Contactors: main / star / delta, three units, mechanical linkage + electrical normally-closed contact double interlock
- Transition: time relay set 5–30 s, switches to full-voltage run once speed approaches rated
- Starting current: about 1/3 of direct-on-line; starting torque drops to 1/3 accordingly (light-load use)
- Protection: thermal overload relay or electronic motor protector — overload, phase loss, imbalance
- Components: Schneider / ABB / Siemens / Chint; brand can be specified, or customer-supplied components shipped to our plant
Specifications
The table below covers 80% of factory distribution room cases. Anything outside it we can still build — those are engineered items, quoted separately, with an indicative price the same day.
| Type | Wall-mounted (≤18.5 kW) or floor-standing (≥22 kW), single-door / double-door |
|---|---|
| Standard sizes (W×D×H) | 600×300×800 (wall-mounted) / 800×600×1600 (floor-standing) mm, custom sizes available |
| Enclosure construction | 1.5–2.0 mm cold-rolled carbon steel, bent and welded, electrostatic powder coated |
| IP rating | IP54 standard / IP65 optional (GB 4208 / IEC 60529) |
| Operator panel | Start / stop pushbuttons, run indicator light, manual / auto selector switch |
| Cable entry | Bottom cable entry, knockouts configured to drawing with cable glands |
| Installation | Wall-mounted / floor-standing against wall; channel steel base under cabinet optional |
| Rated operating voltage | Main circuit AC 380V / 400V, 50 Hz; control circuit AC 220V or DC 24V |
|---|---|
| Applicable motors | Δ-connected (6-terminal) three-phase induction motors, 7.5–90 kW |
| Contactor configuration | Main contactor KM + star KMY + delta KMΔ, AC-3 utilization category |
| Transition method | Automatic switching by time relay, 5–30 s adjustable; optional current relay for current-based switching |
| Switching sequence | Star contactor opens first, then a 50–100 ms dead band before the delta contactor closes — no phase-to-phase short circuit |
| Protection configuration | Thermal overload relay (set at 1.05–1.2 In) or electronic motor protector, with phase-loss protection |
| Indication & metering | Run / fault indicator lights; ammeter / current transformers optional |
| Component brands | Schneider / ABB / Siemens / Chint; customer-supplied components accepted for factory installation |
| Single-motor standard type | One cabinet per motor, pushbutton operation with automatic changeover — the most common configuration |
|---|---|
| Two-speed motor combination type | Star-delta starting and two-speed changeover in one cabinet, for smoke exhaust fan applications (fire alarm interlock supply scope to be confirmed per project requirements) |
| Multi-motor shared type | Two or more small motors share one star-delta starter (each with independent protection) to cut control cost |
| Local + remote control type | Cabinet-front operation and remote signals together, with dry contacts reserved for DCS / PLC |
| Compared with soft start | Choose star-delta for limited budgets and light-load starting; choose VFD when you need speed control and soft stopping |
| Assembly standard | GB/T 7251.1 / IEC 61439-1 |
|---|---|
| Interlock verification | Verify each unit: mechanical interlock linkage operates, electrical interlock contacts switch correctly |
| Routine tests (every unit) | Insulation resistance ≥1 MΩ, power-frequency withstand voltage 2500V/1min, then energize and run 3 complete Y-Δ changeover cycles |
| Temperature rise | Temperature rise at contactor and terminal connections ≤70 K |
| Documents with shipment | Schematic diagram, wiring diagram, terminal list, BOM with brand and model, test report |
Five steps to specify your run
A configuration summary is generated as you go. It travels with your inquiry, saving a round of confirmation.
Build details
Systems have been in service for decades, and the failure points are always the same few: poor busbar contact, water ingress at the door seal, high temperature rise in the correction cabinet, and mis-phased outgoing feeders. The six hard rules below are written for exactly these points — every cabinet can be traced to them.
Every interlock in place
Mechanical linkage plus electrical normally-closed contacts — double interlock. The star and delta contactors can never close at the same time. This is the one safety feature a star-delta cabinet cannot do without.
Changeover dead band
The star contactor opens first, then a dead-band delay before the delta contactor closes. The arc is extinguished before reconnection, eliminating phase-to-phase short circuits and secondary inrush at the moment of changeover.
Energized changeover test on every unit
Before shipment, every cabinet runs 3 complete Y-Δ start and changeover cycles, checked against indicator light sequence and current records. Nothing ships unless it passes.
Protection set to the motor nameplate
The thermal overload relay setting is recorded in the factory documentation based on the motor nameplate current. When the motor is replaced on site, re-verify against the new nameplate.
Wire Number = Circuit Number
Every conductor is fitted with a wire marker, and the number matches the loop number on the schematic one-to-one — no need to trace wires one by one with a multimeter during troubleshooting.
Main circuit and control wiring are routed separately
Power and control cables are run in separate ducts to reduce the effect of electromagnetic interference at switching instants on the timing relay.
Photos & enclosure construction
Below are photos taken in our own shop — from the complete unit down to the internal busbars and secondary wiring. Every build detail can be checked item by item.
Image key: 01–05 are shop photos (the numbers match the shot list). The line drawing shows the front elevation of the enclosure; dimensions match the specification table above.
Where these cabinets go
These are the routine applications — we can talk scheme and configuration directly. For the industry view, see the industry pages.
Centrifugal fan
Low starting torque demand makes star-delta the most economical solution; starting with the damper closed is even smoother.
Centrifugal pumps
Start with the valve closed, open it after running. Star-delta reduces the dual impact on both the piping network and the power grid.
Air compressor light-load starting
Start in star-delta under unloaded condition, complete the transition before the inlet valve fully opens.
Mixers and blenders
Suitable for low-viscosity media that can start unloaded; for high viscosity, use autotransformer or soft starter.
Belt conveyors
Usable for no-load starting; for full-load starting, choose autotransformer step-down or a soft starter cabinet.
Old line retrofit and replacement
Replace a faulty old XJ01 step-down cabinet with star-delta or soft starter; re-check interfaces against the original cables and drawings.
Commercial terms
Specification dated September 2026; quotations follow this.
| Drawings & design | Free |
| MOQ | 1 unit (5 or more recommended for production) |
| Production lead time | 15-25 days after drawing approval |
| on-time delivery | 98% |
| Warranty | 12 months |
| Loading port | Ningbo / Shanghai, China |
| Component brands | Schneider / ABB / Siemens / Chint |
| Factory visit & dispatch confirmation | Factory visits welcome; finished-cabinet photos and video before dispatch |
| Capacity | 5,800+ units / year |
Documents for your engineering team
Selection manual, outline dimensions and RFQ checklist — for the customer's electrical engineer. All three documents are being organized by product line; download links go live once complete.
Six questions procurement and electrical engineers ask most
What motors can use star-delta starting?
It must be a 380V Δ (delta) connected three-phase asynchronous motor with 6 terminals in the terminal box. Motors with a rated Y connection or very low power (≤4 kW) cannot use star-delta switching. Send us a photo of the motor nameplate before ordering and we will verify it for you.
How is the transition time determined?
The rule of thumb is to let the motor accelerate to 80–85% of rated speed before switching. Fans and pumps typically take 5–10 seconds; high-inertia centrifugal equipment takes 15–30 seconds. During first on-site commissioning, fine-tune according to the starting current decay curve, and record the setting in the handover documentation.
How to choose between star-delta and soft starter?
Look at the starting torque demand: for light-load starting such as fans and pumps, star-delta is inexpensive and reliable; if you need a smoother current ramp, soft stopping, or light-load energy savings, choose a soft starter cabinet. In terms of price, star-delta at the same power rating is about half that of a soft starter cabinet.
Can it start under load?
No. Star-delta starting torque is only 1/3 of full voltage, so it can only start unloaded or under light load. For heavy-load starting equipment such as crushers and ball mills, choose an autotransformer step-down starting cabinet (64% torque at the 80% tap) or a soft starter cabinet.
Can one cabinet drive multiple motors?
It can be built as a multi-circuit shared type, but sharing means only one motor can start at a time, and each requires independent protection. If there are many motors and they need to run simultaneously, we recommend an MCC or soft starter cabinet with branch control. We will propose a solution based on your operating sequence.
Why must the star and delta contactors be interlocked?
If both contactors close at the same time, it is a phase-to-phase short circuit on the supply, and the contactors and busbars will burn out within tens of milliseconds. That is why both the mechanical linkage and the electrical normally-closed contact interlock must be present at the same time — missing either one is a hazardous cabinet.
Other cabinet types in the same main circuit
Related products use color-block placeholders for now (product photos not yet complete; they will be replaced together). Internal links will be filled in once live URLs are confirmed.
Send us the motor nameplate and we will first check whether star-delta can be used
Send over the motor nameplate or starting conditions, and we will provide a free starting solution comparison and quotation · reply within 24 hours · build-to-drawing customization supported. Direct from the source factory, MOQ 1 unit, 15–25 day delivery, 1-year warranty.
ISO 9001:2015 · CE(LVD+EMC) · CQC · IP65
When you write, include: single-line diagram or primary scheme, switch room layout, load list, and component brand requirements. You do not need complete drawings — capacity and cabinet type are enough to start.